You mean the pact where she clearly used him for her own desires? The same pact where he did end up outlining his kin and became the only Old God to fully break free from his chains? The same pact that led him to nearly claiming Azeroth only for us to defeat him in the end? The same pact that led to literally every source imaginable (including Xal'atath herself) saying that the Old Gods are dead and that the Black Empire is no more?
Also, his DF cameo just means he's aware of us. Whether that means anything in the current timeline or not is unknown, and I don't think it's really relevant. If you DO connect it to the main timeline (and not just a glimpse into what was, which could lead into an entirely new, separate timeline being made, but whatever...), then that just connects to N'Zoth dreaming of our destiny in BFA, him trying to recruit us during our battle against him, etc.
N'Zoth was very clever, but his arrogance led to his defeat. Unless I'm completely wrong and Blizzard does end up bringing him back, we have no reason to believe the Old God isn't dead. As far as everyone is concerned, he's gone, and Xal'atath outlived the Old Gods (Which was literally the irony of the timewalking cutscene, where Y'Shaarj says everyone but her will claim power and glory, and she is forced to watch everything unfold for eternity).